// 隐式类型转换
// - * /
1 - true 
1 - null 
1 * undefined 
2 * ['5'] 
4/['2']
2/true

// +
'hello'+123
"hello"+[]
"hello"+{}
"hello"+Symbol('world')//报错
123+"hello"
123+'123'
123+true
123+null
123+undefined
123+[]
123+{}

// a == 1 && a == 2 && a == 3
const a = {
    value:[3,2,1],
    valueOf: function () {return this.value.pop(); },
 } 